Abstract

The authors designed, implemented, and tested cryogenic rf filters with zero dc resistance, based on wires with a superconducting core inside a resistive sheath. The superconducting core allows low frequency currents to pass with negligible dissipation. Signals above the cutoff frequency are dissipated in the resistive part due to their small skin depth. The filters consist of twisted wire pairs shielded with copper tape. Above approximately , the attenuation is exponential in , as typical for skin depth based rf filters. By using additional capacitors of per line, an attenuation of at least above can be obtained. Thus, one single filter stage kept at mixing chamber temperature in a dilution refrigerator is sufficient to attenuate room temperature black body radiation to levels corresponding to above about .

Received 26 October 2007Accepted 26 December 2007Published online 25 January 2008

Acknowledgments:

This work was supported primarily by the National Science Foundation under Grant No. DMR-0507931, and by the Department of Energy under Contract No. DE-AC02-76SF00515. We would like to thank Ron Potok for useful discussion and Rob Schoelkopf for providing Ref. 5 before publication.